# What is the meaning of this traffic sign? ("no HM")

**URL:** <https://boards.straightdope.com/t/what-is-the-meaning-of-this-traffic-sign-no-hm/633528>\
**Category:** Factual Questions\
**Created:** [September 3, 2012, 9:25am UTC](https://boards.straightdope.com/t/what-is-the-meaning-of-this-traffic-sign-no-hm/633528 "2012-09-03T09:25:50Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![gatorslap](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gatorslap](https://boards.straightdope.com/u/gatorslap)\
**Post date:** [September 3, 2012, 9:25am UTC](https://boards.straightdope.com/t/what-is-the-meaning-of-this-traffic-sign-no-hm/633528/1 "2012-09-03T09:25:50Z")

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I live in Oakland, CA. I have noticed these signs in Berkeley only, not in Oakland or anywhere else. [Pic](http://image.bayimg.com/kabflaaen.jpg)

What does this mean? And am I an idiot for not knowing (is it common knowledge)? Are these signs common anywhere else?

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**Author:** ![scudsucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scudsucker/32/14101_2.png) [@scudsucker](https://boards.straightdope.com/u/scudsucker)\
**Post date:** [September 3, 2012, 9:42am UTC](https://boards.straightdope.com/t/what-is-the-meaning-of-this-traffic-sign-no-hm/633528/2 "2012-09-03T09:42:44Z")

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Your link is broken.

I would guess, “No heavy machinery”

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**Author:** ![Alley\_Dweller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alley_dweller/32/430_2.png) [@Alley\_Dweller](https://boards.straightdope.com/u/Alley_Dweller)\
**Post date:** [September 3, 2012, 9:44am UTC](https://boards.straightdope.com/t/what-is-the-meaning-of-this-traffic-sign-no-hm/633528/3 "2012-09-03T09:44:45Z")

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[No Hazardous Materials.](http://www.yelp.com/topic/berkeley-mysterious-no-hm-signs-in-berkeley)

[Here is a picture of one](http://www.flickr.com/photos/47278593@N02/4444515226/).

[See Manual of Traffic Signs.](http://www.trafficsign.us/r14.html)

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**Author:** ![Rampant\_Coypu](https://avatars.discourse-cdn.com/v4/letter/r/439d5e/32.png) [@Rampant\_Coypu](https://boards.straightdope.com/u/Rampant_Coypu)\
**Post date:** [September 5, 2012, 7:17am UTC](https://boards.straightdope.com/t/what-is-the-meaning-of-this-traffic-sign-no-hm/633528/4 "2012-09-05T07:17:20Z")

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Similar signs in the Houston area say “HC”. Why the difference. Hazardous loads are banned on several of the freeways here and this is the sign used here.